GB2412148A

GB2412148A - Dual clutch transmission with layshaft having a high/low range gear unit

Info

Publication number: GB2412148A
Application number: GB0504286A
Authority: GB
Inventors: David Allen Janson; Reid Alan Baldwin; Donald Edward Hoffman
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-03-18
Filing date: 2005-03-02
Publication date: 2005-09-21
Anticipated expiration: 2025-03-02
Also published as: GB2412148B; DE102005012535B4; GB0504286D0; DE102005012535A1; US6958028B2; US20050204837A1

Abstract

A dual clutch transmission comprises a layshaft 38 having a range coupler 66 which connects pinions 50, 54 to the layshaft 38, thereby driving pinions 52, 56 fixed to output shaft 12 so as to provide a low range torque path and a high range torque path. A first clutch 14 drives a first input shaft 16 which has gears 28, 30, 32 that mesh with gears 34, 36, 40 mounted on the layshaft 38. A second clutch 18 drives a second input shaft 20 which has gears 22, 24, 26 that mesh with gears 42, 44, 46 also mounted on the layshaft 38. Gears 42, 44, 46 and 34 are releasably engaged by couplers 60, 62 with the layshaft 38 while gears 30, 32 are releasably engaged by a coupler 64 to input shaft 16. The gears 22, 24, 26 are permanently fixed to the input shaft 20 and gear 36 is non- releasably mounted on the layshaft 38. This transmission avoids parasitic losses and provides small torque steps during launch and economic fuel savings.

Description

A MULTI-SPEED TRANSMISSION FOR A MOTOR VEHICLE

This invention relates to transmissions having a layshaft kinematic arrangement and in particular to such a transmission having one or more input clutches but no torque converter.

Automatic transmissions for transmitting power between an input and an output, either over a continuously variable lo range of speed ratios or in discrete step changes among speed ratios, have associated with them several sources of parasitic losses, which adversely affect fuel economy.

These losses are associated with a torque converter, open friction clutches and brakes, hydraulic pump, and gear meshes.

To improve fuel economy in a motor vehicle having an automatic transmission, an automated shift manual (ASM) transmission can be used to eliminate or substantially reduce all of these parasitic losses except gear mesh losses. An ASM transmission generally performs gear ratio changes by first interrupting torque transmitted from the engine to the transmission input, preparing the transmission components associated with the next speed ratio by moving couplers, and then restoring torque. A primary functional feature of ASM transmissions is the need to interrupt power transmitted from the engine to the transmission input shaft before or during each gear ratio change because the couplers cannot be moved while transmitting power.

Dual clutch layshaft transmissions are essentially two ASM transmissions, one providing odd numbered gears and one providing even numbered gears. Shifts between odd numbered gears and even numbered gears can be accomplished without interrupting power flow. While operating in an odd gear, the couplers can be moved to configure the transmission for the next even gear. Dual clutch transmissions have - 2 parasitic losses only slightly higher than ASM transmissions.

Layshaft automatic transmissions offer significant efficiency improvements over conventional step-change automatic transmissions with torque converters. Especially when applied to trucks, however, they must produce more torque multiplication than would be required of a transmission having a torque converter to avoid dissipating lo excessive energy in the clutch during launch of the vehicle from a stopped condition. This requirement for greater torque multiplication in the gearbox also compensates for the torque multiplication that a torque converter produces at lower speeds.

In order to share energy between the dual start-up clutches during launch, it is desirable to have small torque ratio steps between the launch gear ratio and the next higher gear ratio. But providing a large torque ratio span with relatively small ratio steps usually requires a large number of gears and couplers. It is preferable to minimize the number of gears and couplers to reduce package space and to lower cost.

It is an object of this invention to provide an improved multi-speed automatic transmission for a motor vehicle.

According to one embodiment of the invention there is provided a power transmission for producing multiple speeds, comprising an input shaft, an output, a layshaft, a first pinion-gear pair for transmitting torque in a first group of multiple speeds, including a pinion secured to the input shaft and a gear journalled on the layshaft and driveably connected to the pinion a first coupler secured to the layshaft for releasably coupling the gear of the first pair to the layshaft, a high range torque path driveably connected to the output and a low torque path driveably connected to the output and a range coupler secured to the layshaft for releasably coupling alternately the layshaft to the low range torque path and the high range torque path.

Preferably, the layshaft is disposed parallel to the input shaft.

The transmission may include a range gear unit lo providing the low range torque path and the high range torque path.

The transmission may further comprise an input to the transmission and a clutch driveably connected to the input for alternately connecting and disconnecting the input and the input shaft.

The transmission may further comprise a second input shaft, a clutch driveably connected between the input and the input shaft for alternately connecting and disconnecting the input and the input shaft, a second clutch driveably connected between the input and the second input shaft for alternately connecting and disconnecting the input and the second input shaft and a second pinion-gear pair for transmitting torque in a second group of multiple speeds including a pinion secured to the second input shaft and a gear journalled on the layshaft and driveably connected to the pinion of the second pair.

The transmission may further comprise a second coupler secured to the layshaft for releasably coupling the gear of the second pair to the layshaft.

The transmission may further comprise a third pinion gear pair for transmitting torque in a third group of multiple speeds including a pinion secured to the second input shaft and a gear journalled on the layshaft and 4 - driveably connected to the pinion of the third pair wherein the first coupler releasably couples the gear of the first pair and gear of the third pair alternately to the layshaft.

The transmission may further comprise a fourth pinion gear pair for transmitting torque in a speed other than a speed of the first, second or third groups including a pinion journalled on the second input shaft and a gear secured to the layshaft and driveably connected to the lo pinion of the fourth pair, a third coupler secured to the second input shaft for releasably coupling the pinion of the fourth pair to the second input shaft.

The transmission may further comprise a second layshaft, a fifth piniongear pair for transmitting torque in a speed other than a speed of the first, second or third groups including a pinion journalled on the second input shaft and a gear secured to the second layshaft and driveably connected to the pinion of the fifth pair and wherein the third coupler releasably couples the pinion of the fourth pair and the pinion of the fifth pair alternately to the second input shaft.

The transmission may further comprise a second layshaft and the low range torque path comprises a sixth pinion-gear pair including a pinion secured to the second layshaft and a gear secured to the output and driveably connected to the pinion of the sixth pair and the high range torque path comprises a seventh pinion-gear pair including a pinion journalled on the layshaft and a gear secured to the output and driveably connected to the pinion of the seventh and the range coupler releasably couples alternately the layshaft to the pinion of the sixth pair and the pinion of the seventh pair.

Preferably, the transmission may further comprise a second layshaft and the low range torque path comprises a - 5 - sixth pinion-gear pair including a pinion secured to the second layshaft and a gear secured to the output driveably connected to the pinion of the sixth pair and having a rotational speed that is less than the speed of the pinion of the sixth pair and the high range torque path comprises a seventh pinion-gear pair including a pinion journalled on the layshaft and a gear secured to the output driveably connected to the pinion of the seventh and having a rotational speed that is greater than the speed of the lo pinion of the seventh pair and the range coupler releasably couples alternately the layshaft to the pinion of the sixth pair and the pinion of the seventh pair.

According to one embodiment of the invention there is provided a multispeed power transmission, comprising first and second input shafts, an output, a layshaft, a first pinion-gear pair including a pinion secured to the first input shaft, and a gear journalled on the layshaft and driveably connected to the pinion, a coupler for releasably coupling the gear to the layshaft, a high range torque path driveably connected to the output, a low range torque path driveably connected to the output, a range coupler for driveably connecting the layshaft alternately to the high range torque path and the low range torque path and a bridge coupler for releasably coupling the first input shaft to the low range torque path. The transmission may further comprise a second input shaft a second pinion-gear pair including a second pinion secured to the second input shaft and a second gear journalled on the layshaft and driveably connected to the second pinion and a second coupler for releasably coupling the second gear to the layshaft. In addition the transmission may have an input shaft and the layshaft may be disposed substantially parallel to the input shaft. The first and second pinion-gear pairs may have a pinion secured to the input shaft and a gear journalled on the layshaft. A first coupler secured to the layshaft is provided for releasably coupling alternately the gear of the 6 - first pair and the gear of the second pair to the layshaft and a range gear unit is used to provide the low range torque path and the high range torque path.

A transmission according to this invention provides multiple forward gear ratios, yet it has a small number of gears and couplers because a coupler selects between high and low range output ratios.

One of the forward ratios avoids transmitting torque through the range select coupler. While operating in that gear and without interrupting power flow between the engine and the transmission input, the state of the range coupler can be changed to the high range in preparation for an upshift, and to the low range in preparation for a downshift.

Furthermore, this transmission reuses some of the pinion-gear meshes to produce multiple gear ratios, resulting in a low number of gears and couplers for the number of gear ratios produced.

Gear ratio changes are accomplished through the use of couplers, such as synchronizers or dog clutches, which mutually driveably connect components operative in each speed ratio. The couplers produce very little drag loss when engaged, and do not require a continuous supply of power to stay engaged.

The invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a schematic diagram showing a gear arrangement of a transmission according to the present invention; 7 - Figure 2 is a chart containing an example of the number of teeth for each of the gears and pinions of the transmission shown in Figure 1; and Figure 3 is a chart containing the torque ratios between the input and output and steps between the torque ratios for each of the forward gears and the reverse gear of the transmission of Figure 1, the gears and pinions having the number of teeth shown in Figure 2.

Referring now to Figure 1, a transmission according to the present invention includes an input 10 for driveably connecting a power source such as an internal combustion engine or electric motor to the transmission, and an output 12 for driving a load, such as the driven wheels of a motor vehicle, through a powertrain that may include a drive shaft, differential mechanism, and axle shafts.

A first friction clutch 14 alternately connects and disconnects a first input shaft 16 as clutch 14 is engaged and disengaged, respectively. A second friction clutch 18 alternately connects and disconnects a second input shaft 20 as clutch 18 is engaged and disengaged, respectively.

Pinions 22, 24, 26 are secured to input shaft 20, which is supported for rotation on a transmission case about a first axis. Pinion 28 is secured to the input shaft 16, and pinions 30 and 32 are journalled on input shaft 16.

The layshaft 38 is arranged substantially parallel to the axis of the input 10 and input shafts 16, 20.

The pinion 22 is in continuous meshing engagement with gear 42, which is journalled on layshaft 38 and the pinion 24 is in continuous meshing engagement with gear 44, which is journalled on layshaft 38. - 8 -

The pinion 28 is in continuous meshing engagement with gear 34, which is journalled on layshaft 38 and the pinion is in continuous meshing engagement with gear 36, which is secured to layshaft 38.

The pinion 32 is in continuous meshing engagement with gear 40, which is secured to a second layshaft 48 and the reverse pinion 26 is in continuous meshing engagement with an idler gear (not shown) which in turn is in continuous lo meshing engagement with reverse gear 46, which is journalled on layshaft 38.

The layshafts 38 and 48 are preferably arranged concentrically about a second axis.

A low range pinion 50 secured to layshaft 48 is in continuous meshing engagement with a low range output gear 52, which is secured to output 12 and a high range pinion 54, which is journalled on layshaft 38, is in continuous meshing engagement with a high range output gear 56, which is secured to output 12.

Four couplers 60, 62, 64 and 66 are preferably synchronizers of the type used in automotive manual transmissions to connect a gear or pinion to a shaft, after synchronizing the speed of the shaft and that of the pinion or gear. Each coupler may also disconnect the shaft and the associated pinion or gear. An example of such a synchronizer is disclosed in U.S. Patent 4,222,281.

Alternatively, each coupler may be a dog clutch having teeth that are engaged with dog teeth on a gear or pinion.

This invention may use couplers in any combination of synchronizers and dog clutches. Each coupler is secured by a hub to an input shaft or to layshaft 38. For example, coupler 60 is secured by hub 68 to layshaft 38 for rotation with the layshaft. - 9 -

In the case where a coupler is a synchronizer, it is provided with a conical surface, which engages mutually with a corresponding conical surface located on a pinion or gear s adjacent the synchronizer. When the coupler 60 is engaging with either of its adjacent gears 42, 44, these conical surfaces are forced together into frictional contact, and that frictional engagement synchronizes the speed of the gear to that of layshaft 38. Each synchronizer is equipped lo with a sleeve 70 supported on the hub 68 for sliding movement leftward and rightward into engagement with the conical surfaces and dog teeth carried on the adjacent gear and sprocket. When the dog teeth of the sleeve 70 engage those of the gear, the layshaft 38 is driveably connected to the gear.

In the case where a coupler is a dog clutch, displacement of the sleeve 70 in opposite axial directions causes mutual engagement of dog teeth formed on the sleeve with dog teeth carried on the gear being engaged 42, 44, such that a drive connection is made between layshaft 38 and the gear. This occurs without first synchronizing the rotational speed of the layshaft with the speed of the gear.

In Figure 1, the couplers 60-66 are shown in a neutral position, between the left-hand and right-hand extremities of travel of the connecting sleeve carried on the hub of the coupler.

Engagement of the sleeve with dog teeth carried on the gear or pinion associated with the coupler completes a drive connection to the shaft, to which the hub of the coupler is secured. The hubs of the couplers 60, 62, and 66 are secured to layshaft 38 and the hub of the coupler 64 is secured to shaft 16. - 10

Coupler 60, located between gears 42, 44, releasably connects alternately those gears to layshaft 38, and coupler may be disengaged from both gears. Coupler 62, located between gears 46, 34, releasably connects alternately those gears to layshaft 38, and coupler 62 may be disengaged from both gears. Coupler 64, located between pinions 30, 32, releasably connects alternately those pinions to shaft 16, and coupler 64 may be disengaged from both pinions.

Range coupler 66 located between pinions 50, 54, releasably connects layshaft 38 alternately to those pinions depending on the selected range. The coupler 66 is disengaged from both pinions for operation in fourth gear.

Operation of the transmission will be discussed next with reference to the positional state of the coupler sleeves and the applied and released state of clutches 14 and 18.

When the transmission operates in first gear through third gear and in reverse drive, range coupler 66 is in the low range, i.e., its sleeve is moved leftward to connect low range pinion 50 and layshaft 38. When the transmission operates in the fifth through eighth forward gears, range coupler 66 is in the high range, i.e., its sleeve is moved rightward to connect high range pinion 54 and layshaft 38.

When the transmission operates in fourth gear, the coupler 66 is in the neutral state, disconnected from pinions 50 and 54. While operating in fourth gear, the state of range coupler 66 can be changed to the high range in preparation for an upshift, or the state of range coupler 66 can be changed to the low range in preparation for a downshift.

The first forward gear ratio is produced by first moving the selector sleeve of coupler 60 leftward to connect gear 42 to layshaft 38, and then engaging friction clutch 18. The speed of gear 42 is reduced and the torque it transmits is increased relative to those of the input 10. A second speed reduction and torque multiplication occurs in the low range, where pinion 50 drives gear 52 and output 12 at a reduced speed relative to that of layshaft 38. The output 12 is driven at a torque ratio of 5.343 using the gear and pinion sizes of Figure 2.

lo The transmission produces an upshift to the second gear from the first gear by moving the sleeve of coupler 62 rightward, thereby connecting gear 34 to layshaft 38.

Disengaging clutch 18 and engaging clutch 14 transfers the power to pinion 28 and gear 34. Returning coupler 60 to the neutral state completes the upshift. A speed reduction and torque multiplication occurs in the low range, where pinion drives gear 52 and output 12 at a reduced speed relative to that of layshaft 38. The output 12 is driven at a torque ratio of 3.966 using the gear and pinion sizes of Figure 2.

The transmission produces an upshift to third gear from second gear by moving the sleeve of coupler 60 rightward, thereby connecting gear 44 to layshaft 38. Disengaging clutch 14 and engaging clutch 18 transfers the power to pinion 24 and gear 44. Returning coupler 62 to the neutral state completes the upshift. A second speed reduction and torque multiplication occurs in the low range, where pinion drives gear 52 and output 12 at a reduced speed relative to that of layshaft 38. The output 12 is driven at a torque ratio of 3.065 using the gear and pinion sizes of Figure 2.

The transmission produces an upshift to fourth gear from third gear by moving the selector sleeve of coupler 64 rightward to driveably connect pinion 32 to second input shaft 16. Then disengaging clutch 18 and engaging clutch 14 transfers power to pinion 32 and gear 40. Returning 12 couplers 60 and 66 to the neutral state completes the upshift.

The gear 40 is overdriven by pinion 32 and a speed reduction and torque multiplication occurs in the mesh of pinion 50 and gear 52. The coupler 66 need not be engaged in fourth gear because gear 40 and pinion 50 are both continuously secured to layshaft 48. The output 12 is driven at a torque ratio of 2.106 using the gear and pinion sizes of Figure 2.

The transmission is prepared for an upshift to the fifth speed ratio by moving the selector sleeve of coupler 66 rightward to driveably connect gear 54 to layshaft 38, and by moving the selector sleeve of coupler 60 leftward to driveably connect gear 42 to layshaft 38. Then engaging clutch 18 and disengaging clutch 14 transfers the power to pinion 22, gear 42, pinion 54 and gear 56. Returning coupler 64 to the neutral position completes the upshift. A first speed reduction occurs at the mesh of pinion 22 and gear 42 and a speed increase occurs at the mesh of pinion 54 and gear 46. Output 12 is driven at a lower speed than that of input. The torque ratio is 1.478 using the gear and pinion sizes of Figure 2.

The transmission produces an upshift to sixth gear from fifth gear by moving the selector sleeve of coupler 62 rightward to driveably connect gear 34 and layshaft 38.

Then disengaging clutch 18 and engaging clutch 14 transfers power to pinion 28 and gear 34. Returning coupler 60 to the neutral state completes the upshift. Layshaft 38 is driven at a lower speed than that of input 10 due to the mesh of pinion 28 and gear 34, and gear 56 and output 12 are driven at a higher speed than that of layshaft 38. The torque ratio is 1.097 using the gear and pinion sizes of Figure 2. - 13

The transmission produces an upshift to seventh gear from sixth gear by moving the selector sleeve of coupler 60 rightward thereby driveably connecting gear 44 and layshaft 38. Then engaging clutch 18 and disengaging clutch 14 transfers power to pinion 24 and gear 44. Returning coupler 62 to the neutral position completes the upshift. Layshaft 38 is driven at a lower speed than that of input 10 due to the mesh of pinion 24 and gear 44, and gear 56 and output 12 are driven at a higher speed than that of layshaft 38 and lo input 10. The torque ratio is 0.848 using the gear and pinion sizes of Figure 2.

The transmission produces an upshift to eight gear from seventh gear by moving the selector sleeve of coupler 64 leftward, thereby driveably connecting pinion 30 and input shaft 16. Then disengaging clutch 18 and engaging clutch 14 transfer power to pinion 30 and gear 36. Layshaft 38 is driven at a faster speed than that of input 10 due to the mesh of pinion 30 and gear 36. Gear 56 and output 12 are driven at a higher speed than that of layshaft 38 and input 10. The torque ratio is 0.649 using the gear and pinion sizes of Figure 2.

The transmission produces reverse drive by moving the selector sleeve of range coupler 66 leftward to the low range position, thereby connecting pinion 50 and layshaft 38, and moving the selector sleeve of coupler 62 leftward to driveably connect reverse output gear 46 and layshaft 38.

Then clutch 18 is engaged and clutch 14 is disengaged. A first speed reduction occurs due to the drive connection between pinion 26 and gear 46, which is driveably connected through couplers 62 and 66 and layshaft 38 to pinion 50. A second speed reduction is produced at the mesh of pinion 50 and gear 52. The torque ratio is 4.405 using the gear and pinion sizes of Figure 2. - 14

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

Claims

Claims 1. A power transmission for producing multiple speeds, comprising

an input shaft, an output, a layshaft, a first pinion-gear pair for transmitting torque in a first group of multiple speeds, including a pinion secured to the input shaft and a gear journalled on the layshaft and driveably connected to the pinion a first coupler secured to the layshaft for releasably coupling the gear of the first lo pair to the layshaft, a high range torque path driveably connected to the output and a low torque path driveably connected to the output and a range coupler secured to the layshaft for releasably coupling alternately the layshaft to the low range torque path and the high range torque path.
2. A transmission as claimed in claim 1 wherein the layshaft is disposed parallel to the input shaft.
3. A transmission as claimed in claim 1 or in claim 2 wherein the transmission includes a range gear unit providing the low range torque path and the high range torque path.
4. A transmission as claimed in any of claims 1 to 3 further comprising an input to the transmission and a clutch driveably connected to the input for alternately connecting and disconnecting the input and the input shaft.
5. A transmission as claimed in claim 4 wherein the transmission further comprises a second input shaft, a clutch driveably connected between the input and the input shaft for alternately connecting and disconnecting the input and the input shaft, a second clutch driveably connected between the input and the second input shaft for alternately connecting and disconnecting the input and the second input shaft and a second pinion-gear pair for transmitting torque in a second group of multiple speeds including a pinion - 16 secured to the second input shaft and a gear journalled on the layshaft and driveably connected to the pinion of the second pair.
6. A transmission as claimed in claim 5 wherein the transmission further comprises a second coupler secured to the layshaft for releasably coupling the gear of the second pair to the layshaft.

lo
7. A transmission as claimed in claim 5 or in claim 6 wherein the transmission further comprises a third pinion gear pair for transmitting torque in a third group of multiple speeds including a pinion secured to the second input shaft and a gear journalled on the layshaft and driveably connected to the pinion of the third pair wherein the first coupler releasably couples the gear of the first pair and gear of the third pair alternately to the layshaft.
8. A transmission as claimed in claim 7 wherein the transmission further comprises a fourth pinion-gear pair for transmitting torque in a speed other than a speed of the first, second or third groups including a pinion journalled on the second input shaft and a gear secured to the layshaft and driveably connected to the pinion of the fourth pair, a third coupler secured to the second input shaft for releasably coupling the pinion of the fourth pair to the second input shaft.
9. A transmission as claimed in claim 7 or in claim 8 wherein the transmission further comprises a second layshaft, a fifth pinion-gear pair for transmitting torque in a speed other than a speed of the first, second or third groups including a pinion journalled on the second input shaft and a gear secured to the second layshaft and driveably connected to the pinion of the fifth pair and wherein the third coupler releasably couples the pinion of - 17 the fourth pair and the pinion of the fifth pair alternately to the second input shaft.
10. A transmission as claimed in any of claims 5 to 9 wherein the transmission further comprises a second layshaft and the low range torque path comprises a sixth pinion-gear pair including a pinion secured to the second layshaft and a gear secured to the output and driveably connected to the pinion of the sixth pair and the high range torque path lo comprises a seventh pinion-gear pair including a pinion journalled on the layshaft and a gear secured to the output and driveably connected to the pinion of the seventh and the range coupler releasably couples alternately the layshaft to the pinion of the sixth pair and the pinion of the seventh pair.
11. A transmission as claimed in any of claims 5 to 10 wherein the transmission further comprises a second layshaft and the low range torque path comprises a sixth pinion-gear pair including a pinion secured to the second layshaft and a gear secured to the output driveably connected to the pinion of the sixth pair and having a rotational speed that is less than the speed of the pinion of the sixth pair and the high range torque path comprises a seventh pinion-gear pair including a pinion journalled on the layshaft and a gear secured to the output driveably connected to the pinion of the seventh and having a rotational speed that is greater than the speed of the pinion of the seventh pair and the range coupler releasably couples alternately the layshaft to the pinion of the sixth pair and the pinion of the seventh pair.
12. A multi-speed power transmission substantially as described herein with reference to the accompanying drawing.